X-ray differential phase-contrast imaging (DPCI) visualizes the phase information of coherent X-rays passing a scanned object. In addition to classical X-ray transmission imaging, DPCI may determine not only the absorption properties of the object along a projection line, but also the phase-shift of the transmitted X-rays, and thus may provide valuable additional information. After the object, a phase-shifting grating (also known as phase grating) is placed, working as a beam splitter. The resulting interference pattern contains the required information about the beam phase-shift in the relative position of its minima and maxima, typically in the order of several micrometers. Since a common X-ray detector, which may have a typical resolution in the order of 150 μm, may not be able to resolve such fine structures, the interference is sampled with a analyzer grating (also known as absorber grating), which features a periodic pattern of transmitting an absorbing strip with a periodicity similar to that of the interference pattern. The similar periodicity produces a Moiré pattern behind the grating with a much larger periodicity, which is detectable by a common X-ray detector. To obtain the differential phase-shift, the absorber grating and the phase grating are shifted laterally with respect to each other by fractions of the grating pitch, which is typically of the order of 1 μm. This movement is referred to as phase stepping or phase scanning. The phase-shift can be extracted from the particular Moiré pattern measured for each position of the absorber grating.
For example, in EP 1 731 099 A1, an X-ray interferometer arrangement is shown that can be used to execute grating-based differential phase-contrast imaging. The X-ray interferometer comprises an incoherent X-ray source with a source grating and a detector arrangement with a phase grating and an absorber grating.